Our recent work dealing with number and location of 0-antigen insertion sites into the cell surface of Salmonella has substantiated our earlier findings that the lipopolysaccharide insertion takes place at 20 to 40 discrete areas of the cell surface. We are now studying the production sites of capsular antigens in temperature-sensitive mutants of Escherichia coli. Since the capsular polysaccharide serves as receptor for capsule-specific phages, we will employ phage adsorption as a tool to discern early stages of production of the antigen, in addition to immunological and electron microscopic tehniques. In preliminary experiments the export (or insertion) sites of capsular antigen were found in the mutants to be few in numbers (about 20 per growing cell), and became observable after 10 to 15 minutes following shift-down to permissive temperatures. This work will be continued to find out 1) the mode by which capsule specific phages adsorb to their receptor and 2) by which they penetrate the wild type polysaccharide capsule. BIBLIOGRAPHIC REFERENCES: 1) M.E. Bayer and R.W. DeBlois (1974) Diffusion constant and dimension of bacteriophage X174 as determined by self-beat laser light spectroscopy and electron microscopy. J. Virol. approximately 14:975-980. 2) M.E. Bayer. (1974) Ultrastructure and organization of the bacterial envelope. Annals of the N.Y. Acad. of Sciences 235:6-28.